In the processing of semiconductor wafers and other semiconductor pieces it is typical to perform steps which chemically etch or otherwise remove semiconductor material from the surfaces of the pieces being processed. In the processing of silicon wafers it is common to use an aqueous mixture of hydrogen fluoride to remove silicon and silicon oxide layers. Such aqueous hydrofluoric acid mixtures are effective at performing etches which remove silicon at relatively high etch rates thus speeding processing of the wafers. Vapor phase mixtures of hydrogen fluoride and water have also been used.
In such processing the uniformity of etching is an important consideration which in-part governs the suitability of results associated with a particular process. Processes which otherwise may be conceptually sound will not be commercially viable unless adequate uniformity can be achieved. Uniformity in the etching rates from point to point across the wafer are now preferably on the order of 10 angstroms (10.sup.-9 meters) or better. To achieve such high degrees of uniformity in etch rates across the wafer is a constant challenge. Even relatively minor variations in processing parameters can have dramatic effects which render the processed semiconductor piece worthless. Such processing is also very sensitive to variations in the repeatability of etch rates between wafers within a batch or between different batches of wafers run using what appears to be the same process and processing parameters. These considerations thus make it extremely difficult to achieve improved processing.
Further complicating the problems of uniformity and repeatability is the desire by most semiconductor device production companies for batch production processes. Batch production processes have the inherent advantage of allowing more throughput per unit of time when conducting the same processing step. However, batch mode processing has the disadvantage that the wafers or other semiconductor pieces are typically held within the processing chamber in a closely spaced parallel processing array configuration. This configuration limits the access of processing fluids to the faces of the wafers which are within the processing array. Thus there are increased challenges with regard to achieving uniformity across the wafer surface because the edges of the disk-shaped wafers are more accessible and the interior areas are less accessible. These factors further complicate the processor's ability to achieve repeatable processing results between different batches because of localized and transitory effects associated with processing multiple batches each containing multiple wafers or other pieces.
Another important consideration in the processing of semiconductor pieces is the need to maintain levels of contamination very low. Even relatively small contaminants of approximately 0.2-0.5 microns can be problematic in the resulting devices being produced. Prior etching technologies for silicon and other semiconductor materials have frequently included one or more hydrogen fluoride processing steps. When a hydrogen fluoride step is performed as a last step in the etching or larger process, this typically results in a hydrophobic silicon surface. Such hydrophobic semiconductor surfaces are more susceptible to contamination, particularly contamination due to particles becoming adhered to the surface of the wafer. In some processing it is mandatory that the silicon surface be cleared of all silicon oxide. This is frequently done using aqueous hydrogen fluoride rinses which render the resulting surface hydrophobic and more susceptible to particle contamination. Thus hydrofluoric acid processing may result in the addition of numerous particles (0.2 micron or larger), such as 100-10,000 particles per wafer.
Thus there has been a longstanding need for hydrofluoric acid and other semiconductor removal processing which has an improved ability to resist contamination, and in particular contamination due to particle additions. Such ability has been needed while also maintaining uniformity and repeatability in the removal rates of the semiconductor materials.
There has also been a long-felt need in the art of semiconductor processing for improved processes and apparatus for providing vapor phase chemical processing. Vapor phase processing can be particularly difficult in some chemistries. In all chemistries there are particular concerns associated with generation of vapor phases of the processing chemicals in such a manner as to achieve vapor phases which are homogeneous. The homogeneity desired is sometimes a matter of achieving homogeneous vapor concentrations of a single constituent. Still more challenging is the difficulty in achieving homogeneous vapor concentrations when there are multiple chemical constituents in additional to air, nitrogen or other underlying gas with which the vapors are mixed or carried.
Vapor phase mixtures also typically vary in relative concentrations of the constituents and in other ways different from liquid mixtures from which the vaporous mixtures are generated. For example, the relative amounts of a mixed constituent chemical system when in the liquid state often are different than when these same constituents are transformed to a vapor phase. These variations further increase the challenges for producing uniform and repeatable processing results.
There remains a need in the semiconductor processing industry for improved methods and apparatus for effecting vapor phase processing in a reliable, repeatable and uniform manner.